This invention relates to an electromagnetically operated hydraulic actuator and, more particularly, to an electromagnetic hydraulic driving unit for driving a valve element of a hydraulic control valve, especially an electromagnetically operated hydraulic actuator for driving a actuator piston by an output hydraulic pressure of a pilot control valve driven by electromagnetic plunger means.
Recently, a strong demand for energy saving has been raised in the field of hydraulically controlled mechanical devices. Above all it is desired that power consumption of the electromagnetic valves frequently used in the hydraulic systems be reduced drastically.
To this end, a variety of pilot driven electromagnetic valves have been devised.
The pivot driven electromagnetic valve is roughly composed of a valve portion and an actuator portion for driving the valve portion. The actuator portion is generally composed of an electromagnetic plunger called "solenoid apparatus" and an actuator piston. The electromagnetic plunger employed in the typical conventional device is similar to that of the commonly employed electromagnetic valve and comprised of a solenoid coil, a stationary magnetic core and a movable magnetic core. Thus the pilot control valve and the actuator piston are arranged in one pilot body block, and both the pilot body and the electromagnetic plunger blocks are mounted to one side of the valve portion.
Therefore, the prior-art hydraulic actuator cannot be reduced in size beyond a certain lower limit. In addition, response characteristics of the prior-art actuator are lowered because the hydraulic communication between the pilot control valve and the actuator piston is established by oil conduits provided in the blocks.